Ion thrusters are currently used for spacecraft control on some communications satellites. Some existing systems operate by ionizing xenon gas and accelerating it across two or three charged molybdenum grids. As the ions pass through these grids, small amounts of molybdenum are sputtered off to deposit on the downstream grids. Over time, these deposits can grow large enough to flake off and cause a short circuit between the grids, shutting down the thruster. When this occurs, the thruster must be turned off so that the grids can be cleared to remove the short circuit. Grid clear circuitry is employed to apply energy through the short, causing the material to be burned off.
FIG. 1 is a schematic diagram of a contaminated ion propulsion grid within an ion thruster. When the thruster is operating, ionized gas 102 is accelerated across two or more charged grids 104. However, deposits can accumulate on the grids 104 to a point where a short circuit 106 is created, which reduces or eliminates the effectiveness of the thruster.
Prior art grid clear circuits employ a dropping resistor 110 coupled to a voltage source 108 (e.g., the spacecraft bus voltage) to clear the grids 104. The voltage source 108 is applied (through the dropping resistor 110) to the shorted grids 104. However, there is still a need for other grid clearing processes and circuitry that would provide improvements over prior art systems and provide additional benefits or advantages (e.g., reduce operating or maintenance costs, increase thruster service life, increase grid service life, reduce energy requirements, for example, for clearing a grid, but still effectively reduce or remove contamination on grid surfaces or grid systems.